比如

ping www.baidu.com

会显示：ping: www.baidu.com: Name or service not known

解决方法

sudo gedit /etc/NetworkManager/NetworkManager.conf

将managed的false改为true，最终修改为：

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=true

[device]
wifi.scan-rand-mac-address=no

然后重启一下网络服务：

sudo service network-manager stop
sudo rm /var/lib/NetworkManager/NetworkManager.state
sudo service network-manager start

然后就OK了